The invention relates to a method of manufacturing a lithium battery comprising a stack of a negative electrode, a separator, and a positive electrode, which method comprises applying negative electrode material onto a negative current collector so as to form the negative electrode, applying positive electrode material onto a positive current collector so as to form the positive electrode, and arranging a separator between the negative electrode and the positive electrode, wherein the method comprises the following steps:
a) producing a pattern of holes in the negative electrode;
b) producing a pattern of holes in the positive electrode; applying a polymeric material on the stack, so that the polymeric material penetrates the holes by which the negative electrode, the positive electrode and the separator are stuck and pressed together.
Due to a growing market for lightweight, portable cordless consumer products, such as CD-players, mobile telephones, laptop computers and video cameras, there is an increased need for high-density batteries. Specifically, very thin and flexible batteries are required. In order to provide for an acceptable portability, the batteries contained in said consumer products should provide the necessary amount of energy at the smallest possible weight and volume. Lithium is a very advantageous material for use in batteries in which a high energy density at a minimum weight is required. However, the thinner the battery gets, the more difficult the application of pressure, which is needed to maintain sufficient contact between the respective components of the battery, becomes.
A method of manufacturing a lithium battery according to the preamble is known from the International patent application with publication number WO 00/04601.
The battery which is obtained by said method has thin and flexible form and provides at the same time a very high energy density. Moreover, the contact between the electrodes and the separator is obtained and maintained in a very efficient way. The battery can be packed in a thin walled can, as the wall of such can is not needed to maintain sufficient pressure on the respective components of the battery. In one of the methods according to the International application WO 00/04601, a film of a polymeric material is applied onto both sides of the stack, and said polymeric film is subjected to heat and pressure. As a result thereof the polymeric material melts and penetrates into the holes. By said method a battery is obtained with a polymeric film at both sides of the stack as well as polymeric material in each of the holes acting as a plug or rivet and sticking to the respective layers, causing these layers to be bonded together.
Generally, a low temperature processable polymer is used in order to preserve the thermal fuse function of the separator. Such polymer often does not have sufficient mechanical properties at higher temperatures.
It is an object of the invention to provide a method of manufacturing a lithium battery according to the preamble, by which a battery is obtained with improved thermal and mechanical properties of the polymer.
To this end the method of manufacturing a lithium battery according to the preamble is characterized in that after step c) the polymeric material is subjected to a treatment with high energy radiation.
By treating the polymeric material with high-energy radiation the polymeric material is caused to cross-link which enhances its mechanical properties at higher temperatures.
In a particular embodiment the high-energy radiation comprises electron beam radiation. In another preferred embodiment, the radiation is performed by means of gamma-rays.